1. Field of the Invention
The present invention relates to an NMOS device, a PMOS device and a SiGe HBT device and a method of fabricating the same and, more particularly, to an NMOS device, a PMOS device and a SiGe HBT device which are integrated on a silicon on insulator (SOI) and a method of fabricating the same
2. Discussion of Related Art
Typically, gallium arsenide (GaAs)-based compound semiconductors have been employed in fabricating radio frequency (RF) devices for information communication, and complementary metal oxide semiconductor (CMOS) devices have been employed in fabricating analog/digital circuits. Currently, a RF/analog/digital system-on-chip (SoC) is widely being used, and a silicon germanium (SiGe) bipolar complementary metal oxide semiconductor (BiCMOS) device is known to be suitable for fabricating the RF/analog/digital SoC. The SiGe BiCMOS technology is one which integrates a SiGe hetero junction-bipolar transistor (HBT) suitable for an RF/analog circuit and a CMOS device suitable for a digital circuit on a single substrate, and is widely used in fabricating an SoC of communication devices such a cellular phone.
The SiGe HBT is an improvement of a conventional bipolar transistor, and it uses as a base material a SiGe alloy that Ge of 20% is mixed with Si other than silicon (Si). The SiGe HBT has advantages of obtaining a larger current gain than the conventional bipolar transistor and of being able to perform high-speed and high frequency operation in that a base may be thinner by increasing an impurity concentration of the base by 100 times.
Meanwhile, a use of the SOI substrate in the CMOS is increasing due to low power consumption. However, as a gate length is scaled down to less than 100 nm in such structure, an abnormal leakage current is increased due to parasitic bipolar operation between a source and a drain, and a resistance of the source and drain layer and a resistance between the source and drain layer and a contact point with an external metal line are sharply increased, and thus heat in the chip is increased. This becomes an obstacle to practically using the device.